1. Field of the Invention
The present invention relates to a substrate for an organic electroluminescence (EL) device and a method of producing the substrate, an organic EL device, and a display apparatus including the organic EL device.
2. Description of the Related Art
An organic EL device is a device having an emission layer formed of an organic low-molecular weight compound or organic polymer having an EL light emission ability. The organic EL device has, for example, the following characteristics ideal for a display device: the device has a wide view angle because the device is of a selfluminous type, and the device is excellent in impact resistance. Accordingly, researches and developments have been conducted on the device in various fields.
The method for the production of the device, which has been widely studied, is, for example, a vacuum vapor deposition method, an ink-jet method, or a printing method. In a nozzle printing method using solutions each prepared by dissolving an organic EL material in a liquid (SID 05 Digest p. 1192), banks each formed of an organic material on a substrate are subjected to liquid-repellent processing with fluorine plasma generated in a vacuum apparatus so that the liquid organic EL materials are applied in isolation from each other.
In such applying apparatus that continuously applies the liquid organic EL materials, patterning is generally performed by applying each of the liquid organic EL materials between adjacent stripe-shaped banks.
However, such stripe-shaped bank involves the following problem: a solution (liquid organic EL material) diffuses toward the outside of the bank owing to a capillary phenomenon when the solvent of the solution has a small surface tension, or the solution is repelled by the bank so as to be withdrawn into the bank when the solvent of the solution has a large surface tension.
Meanwhile, a solvent having somewhat low volatility must be used for a liquid organic EL material in such application-based apparatus in order that the clogging of an orifice for applying the material due to the drying of the solvent may be suppressed or the planarity of a film formed of the material at the time of the formation of the film may be improved. However, it has been generally known that a solvent having low volatility has a large surface tension, so the withdrawal of the solvent becomes of more serious concern than a solvent having high volatility does. Japanese Patent Application Laid-Open No. 2005-63959 discloses that a diffusion preventing portion is provided for each of the start edge portion and end edge portion of a stripe-shaped bank.
However, merely closing the start edge portion and end edge portion of the bank may be unable to hold a liquid organic EL material at each of the start edge portion and end edge portion of the bank at the time of the application of the material. In addition, the presence of an impurity in the bank involves the following problem: the withdrawal of the material occurs at the position where the impurity is present as an origin, with the result that a film cannot be formed from the material on one entire line.